I’m sure this would work in 2.8 or 2.9+ not sure when it was added could have been 2.8. However you should be running the most recent version of wordpress many security and functionality updates have been released since 2.8. I don’t think that you can disable specific rss categories, this just removes the category feeds from the wp_head. You could however check the category you are in and then run this remove_action if not in a specific category.

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